In a packet transmission network, a network with a wireless line has a small transmittable capacity through only one wireless line. Therefore, a plurality of wireless lines may be bundled into a virtual one line to secure transmission capacity. In other words, the transmittable capacity is secured for the all wireless links by distributing a single traffic into a plurality of wireless lines. This bundling of a plurality of wireless lines is referred to as link aggregation. This link aggregation is specified in IEEE802.3ad.
With reference to the above-mentioned technique, for example, Patent Literature 1 discloses that it is possible to obtain a data rate faster than the data rate which can be realized using a single carrier, by using three carriers whose frequencies are different from each other to perform modulation for and transmit three data streams. Note that when the single data stream is divided into multiple data streams, fragments are formed.